1. Field of the Invention
The present invention relates to an optical disk apparatus and an optical pickup device for recording information on an optical disk or reproducing information therefrom, in particular, an optical disk apparatus and an optical pickup equipped with an optical element for correcting spherical aberration in a beam spot generated due to a thickness error in an optical disk protecting substrate.
2. Related Background Art
Recently, in the technical field in which the recording or reproduction of information signals is effected by using, for example, an optical disk as an information recording medium, the development of an optical disk apparatus having a small size and a large capacity is under way in order to handle high definition still images, moving pictures, etc. An optical disk apparatus is equipped with an optical pickup device for forming a beam spot on the information recording surface of an optical disk, and, as is known in the art, in this optical pickup device, there is generated spherical aberration when a light beam emitted from a light source passes through a transparent protective substrate layer for protecting the information recording layer. As a method of correcting spherical aberration, a method is known according to which an optical element for correction is moved in the optical axis direction.
As a method using such an optical element for correction, for example, Japanese Patent Application Laid-Open No. 2002-312971 proposes use of a device in which there are provided a movable optical element for correcting spherical aberration and a stationary optical element, wherein a movable optical element holder is moved by a DC motor driving force through a driving mechanism, thereby correcting spherical aberration.
Similarly, Japanese Patent Application Laid-Open No. 2003-091847 proposes a device for correcting spherical aberration which uses a concave lens and a convex lens for spherical aberration correction, wherein the concave lens is held by a lens holder, which is driven by a stepping motor, thereby effecting spherical aberration correction.
In the above prior-art techniques, the optical disk is neither accommodated in a cartridge nor reduced in the size and thickness of the pickup device. If such a spherical aberration correcting device is applied to a small and thin optical pickup device which uses a cartridge, such as a portable MD drive, the following problems will be involved.
In the technique as disclosed in Japanese Patent Application Laid-Open No. 2002-312971, the movable optical element holder holding the movable optical element is formed as a cylinder surrounding the periphery of the optical element, and is driven in the optical axis direction of the optical element by a DC motor while guided by a reference shaft. While the thickness of the movable optical element holder with respect to the driving mechanism including the DC motor is not explicitly given here, this holder has a problem that the thickness of the optical element holder in a direction perpendicular to the optical axis of the optical element is rather large with respect to the diameter of the optical element.
Similarly, in the technique as disclosed in Japanese Patent Application Laid-Open No. 2003-091847, the lens holding member for holding the concave lens out of the expander lenses is formed so as to surround the entire periphery of the concave lens, and the outer diameter of the lens holding member is very large as compared with the lens diameter, so that the width of the optical pickup device in a direction perpendicular to the optical axis of the spherical aberration correction lens group is rather large, resulting in a rather large optical pickup device.